This invention relates to an interface circuit, and, more particularly, to an interface circuit to couple a modulated power supply with a fluorescent lamp system, and, even more particularly, to an interface circuit to couple a triac modulated power supply with a compact fluorescent lamp system.
Fluorescent lamps are used both at the office and at home to provide lighting. The fluorescent lamps are typically part of a fluorescent lamp system, which usually includes a converter, and are powered by a power supply such as a conventional 100-120 VAC line source. Power from the line source is provided to the inverter which provides power input at a suitable frequency to the fluorescent lamp. To provide a dimming capability, the power from the line source may be modulated by a modulator, such as a triac phase modulator.
Triac phase modulators typically are used to modulate power provided to resistive loads. However, there may be incompatibility between a triac phase modulator and a capacitive load which is provided with modulated power from such modulator, for example, due to the existence of continuing currents and/or stored voltages when the triac phase modulator is supposed to switch from one conductive state to the other. The result of such incompatibility can stress the triac, the control or gate circuit therefor, or both, which may degrade the operation and longevity of the triac phase modulator circuit and/or capacitive load, for example, a fluorescent lamp system.
Interface circuits have been used to control voltages and currents that occur while power is transferred from such a modulated power supply to the fluorescent lamp system. However, conventional interface circuits have failed to fully compensate for the capacitive nature of the fluorescent lamp system, and do not fully compensate for the rapidly changing voltages and currents that can electrically stress or fatigue various elements of a triac phase modulator and interface circuit. Thus, this sometimes results in premature failures of the modulator, interface circuit and/or fluorescent lamp system. An example of such an interface circuit is presented in U.S. Pat. No. 5,994,848 to Janczak, which discloses an interface circuit connected between a triac dimmer and a compact fluorescent lamp.
Accordingly, there is a need in the art for an interface circuit to provide compatibility between a triac phase modulator and a fluorescent lamp, for example a compact fluorescent lamp.
Thus there is a particular need for an interface circuit for coupling a modulated power supply to a capacitive load including a switching element coupled to the modulated power supply to selectively provide a current path, and a threshold sensing element coupled to the switching element to determine when a threshold is exceeded such that the threshold sensing element controls when the switching element provides the current path.
Thus there is a particular need for an interface circuit including a means for voltage rectifying a modulated power supply, a means for switching, coupled to the means for voltage rectifying; and a means for threshold sensing, coupled to the means for switching.
Thus there is a particular need for a method of coupling a modulated power supply with a capacitive light source load including selectively coupling the modulated power supply to a capacitive light source load, a sensing element coupled to the modulated power supply to determine if a threshold current through the sensing element is exceeded, and discharging at least one charged element when the threshold is not exceeded.